Circular workpieces, or workpieces formed from, or having circular components, for example, in the shape of right cylinders, such as a disk or ring, find use in many applications where the component must be metallurgically hardened to withstand forces applied to the workpiece in the application. For example a metallic disk-shaped component is used in wheel hubs, and complex automotive constant velocity joints. In addition to workpieces that are formed completely in the shape of a right cylinder, complex workpieces can consist of multiple components that include a right cylinder-shaped component such as the gear blank 91 shown in FIG. 1(a). U.S. Pat. No. 3,251,976 illustrates one method of induction heat treating a gear blank. For convenience the above described right cylinder-shaped workpieces, and complex workpieces comprising at least one right cylinder-shaped component, will be referred to as a cylindrical or circular workpiece.
Various types of induction coils can be utilized to induction heat treat a cylindrical workpiece. Since induction heating of a workpiece is dependent upon magnetic flux coupling with portions of the workpiece to induce the eddy current heating in the workpiece, uniform inductive heat treatment throughout the entire workpiece is difficult to achieve with some induction coil arrangements. The inductive heating process is further complicated by the fact that generally heat penetration into the interior of the workpiece is a combination of both inductive eddy current heating inwardly, and then further conductive inward heat transfer from the eddy current regions (controlled by the depth of current penetration) towards the central region of the workpiece, which conductive heating process is known in the art as heat “soaking”
FIG. 1(b) and FIG. 1(c) illustrate one method of inductive heat treatment of cylindrical workpieces. Cylindrical workpieces 90a, 90b and 90c are sequentially fed within two-turn channel inductor 12, which is suitably connected to an alternating current power source. Workpiece flow within the inductor is from left to right as indicated by the arrow at the entry of the induction furnace. A suitable conveyor apparatus 92 (shown diagrammatically) is used to linearly transport the workpieces within the inductor. Side guides 94 can be provided either separate from, or integral to, the conveyor apparatus, to keep the workpieces linearly aligned as they move linearly within the inductor. Since magnetic flux (established by alternating current flow in the inductor) coupling with the cylindrical workpieces is achieved at the sides of the workpieces adjacent to the inductor as illustrated by typical flux lines 96 in FIG. 1(c), inductive eddy current heating (depth of current penetration) is initially concentrated in (dark shaded) regions 90′ as shown for workpiece 90c in FIG. 1(b), with progressive inward heat soaking of the workpieces as they travel within the inductor as shown for workpieces 90a and 90b. Consequently internal heating is uneven through the entire mass of the workpiece, as illustrated by the cooler white regions in each of the workpieces. Rotation of the workpieces during the inductive heating process has been recognized as a solution to the uneven heating but apparatus for accomplishing the rotation are complex and increases the total equipment cost.
One object of the present invention is to provide a simplified apparatus and method for rotation of a cylindrical workpiece during an induction heat treatment process.